Centrifugal casting apparatus

ABSTRACT

A centrifugal casting apparatus is provided for casting concrete, flat surfaced articles such as hollow, square beams; a first mold surface having flat walls for forming the exterior surface of the beam is carried on a set of ring members evenly spaced along the mold enclosure; core members are mounted within the flat walls and spaced therefrom for forming the interior surface of the beam; the core members are shaped and arranged with respect to one another to provide flow passages for the casting material so that when the mold enclosure is rotated about its axis, casting material may be continuously supplied to the interior of the housing and fed to the forming surfaces.

United States atent n 1 Motheral [54] CENTRIFUGAL CASTING APPARATUS [76] Inventor: R. B. Motheral, Rt. 4, Box 130,

. Georgetown, Tex. 78626 [22] Filed: June 17, 1971 [21] Appl.No.: 154,151

[52] US. Cl. 425/435, 249/137, 264/311 [51] Int. Cl. ..B28b 21/30 [58] Field of Search ..425/435; 249/137; 264/311 [56] References Cited' UNITED STATES PATENTS 51 Mar. 27, 1973 Primary Examiner-J. Spencer Overholser Assistant Examiner-B. D. Tobor Att0rney-Cushman, Darby & Cushman [57] ABSTRACT A centrifugal casting apparatus is provided for casting concrete, flat surfaced articles such as hollow, square beams; a first mold surface having flat walls for forming the exterior surface of the beam is carried on a set of ring members evenly spaced along the mold enclosure; core members are mounted within the flat walls and spaced therefrom for forming the interior surface of the beam; the core members are shaped and arranged with respect to one another to provide flow passages for the casting material so that when the mold enclosure is rotated about its axis, casting material may be continuously supplied to the interior of the housing and fed to the forming surfaces.

10 Claims, 5 Drawing Figures PATUHEUMARZHSH SHEET 1 [IF 3 CENTRIFUGAL CASTING APPARATUS The present invention relates to improvements in centrifugal casting apparatus of the type used for forming articles from settable materials such as concrete slurry or the like, and, more particularly, articles having generally flat, oppositely facing surfaces.

BACKGROUND OF THE INVENTION Apparatus for and methods of centrifugal casting have long been known and used to form articles having excellent structural integrity, uniform dimensions and which are capable of withstanding heavy strains in the various structural installations in which they are employed. One of the chief advantages of known centrifugal casting methods resides in the fact that the casting material is highly compacted during the formation of the object by virtue of the centrifugal force exerted on it due to the rotation of the forming mold. As a result of the compression, the object when completed will be substantially free of interstices which would otherwise tend to weaken the object.

The devices proposed by the prior art for carrying out the centrifugal casting of objects have generally utilized a mold pattern that is mounted for rotation about an axis. In some arrangements, the mold pattern is constructed so as to require that an amount of casting material be placed in the mold prior to initiation of the rotation of the mold. However, where the operator of the device fails to supply an accurate quantity of casting material, the resulting cast object will be of inferior quality or even useless for its intended purpose. In addition, in such arrangements, either counterbalancing weights must be used to assure that the rotating body will be maintained in rotational equilibrium or the flowable casting material must be first distributed evenly over the mold pattern prior to initiation of the rotation.

In other casting structures, means have been employed, permitting the introduction of casting material into the mold as the mold is rotated thus obviating the necessity and expense of using counterweights, on the one hand, and the time-consuming task of distributing the material in the mold, on the other. However, the casting structures that have been proposed prior to the present invention have lacked means for controlling the feeding of the casting material to the forming surfaces of the mold and, in addition, have been so constructed as to be capable of forming only one or a very limited variety of different shaped objects.

Generally, the prior art centrifugal casting devices have not been able to be easily adapted to form articles having flat parallel surfaces such as in panels or beams of square, rectangular or triangular cross section both on the interior and exterior surfaces of the beam so that articles of this type have had to be formed by time-consuming static casting methods.

SUMMARY OF THE INVENTION The apparatus of the present invention avoids the foregoing disadvantages by providing a casting enclosure having flat surfaces for forming one surface of an object and core members which are adjustably mounted in the enclosure to form another surface of the article.

In a preferred embodiment, the apparatus of this invention is arranged to form concrete beams which are substantially square or rectangular or triangular in cross section with all of the interior and exterior surface portions of the beams being planar and extending at predetermined angles to each adjacent surface.

By way of example, to cast square beams according to the principles of the present invention, four flat, equally dimensioned wall members are clamped along their edges in the form of an open-ended box-like enclosure which has a centrally located axis of rotation extending longitudinally thereof. Core members each having a longitudinal extent commensurate with that of a wall member are mounted in the enclosure and attached at each of their ends to the ends of the wall members. For forming hollow square beams, the core members are provided each with two sets of flat surfaces. The first set of surfaces is employed to form the interior surfaces and right angled corners of the beam and, to this end, the core members are positioned in the enclosure with these surfaces extending in spaced parallel relation to the respective interior surfaces of the wall members.

The second set of surfaces of the core members are shaped to cooperate with an opposing surface of adjacent core members to form flow passages for the concrete slurry which extend radially from the centrally located axis of rotation of the enclosure to the spaces between the wall members and the first sets of surfaces of the core members.

The enclosure is rigidly but detachably secured at points on its exterior to a plurality of annular ring supports which are spaced along the axis of rotation and which are mounted on rollers. A member of these rollers are drivingly connected by a shaft which is connected to a suitable power source. The ends of the enclosure may be closed by sealing plates one of which is formed with an opening through its center through which a slurry conveyor may be extended to supply cementitious material to the interior of the enclosure during its rotation. In another embodiment, instead of using sealing plates, spacer members or headers are inserted between each of the core members and the interior surfaces of the enclosure to block the flow of slurry in the spaces between the first set of surfaces of the core members and the interior surfaces of the enclosure. These headers may be positioned so as to extend transverse to the longitudinal axis of the enclosure or may be slanted to vary the shape of the ends of the cast object and to permit the casting of objects of varying longitudinal extent.

As will be hereinafter more fully described, the apparatus of this invention is easily adapted to centrifugally cast other objects such as concrete panels, corner panels or steel reinforced articles and to provide such articles in a wide range of dimensions.

One of the objects of the present invention is to provide an apparatus for centrifugally casting articles having substantially flat, oppositely facing surfaces.

Another object of this invention is to provide a centrifugal casting apparatus that can be easily and quickly adapted to mold a variety of differently shaped articles.

A further object of this invention is to provide a centrifugal casting apparatus that can be easily modified to cast a plurality of discrete articles.

These and other objects and attendant advantages will become apparent as consideration is given to the following detailed description and accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in perspective of the molding elements and a portion of the support means of the invention;

FIG. 2 is an end view in elevation of the apparatus of this invention;

FIG. 3 is a top plan view of the apparatus illustrated in FIG. 2 within a part broken away to show an interior portion of the enclosure;

FIG. 4 is a view in perspective of one of the core members; and

FIG. 5 is an elevational view of one of the closure plates of the present invention.

DETAILED DESCRIPTION OF THE INVENTION With reference now to the drawings wherein like numerals designate corresponding parts throughout the several views, there is illustrated in FIG. 1 a mold enclosure generally designated at 10, and which consists of four, flat wall sections l2, l3, l4 and 15. The wall sections are securely joined along their longitudinal edges by any suitable means such as an angle bar 16 to which each of the wall sections is bolted to form the generally cross-sectionally square enclosure 10. Preferably, the wall sections are made from stiff sheet metal, but it will be understood that other suitable materials may also be employed. Also, it is within the contemplation of this invention that other polygonal articles can be made by forming the enclosure with the desired number of wall sections.

As shown in FIG. 1, a plurality of annular rings, one of which is indicated at 18, are fixed about the exterior of the enclosure and evenly spaced along its longitudinal axis. A plurality of collar members one of which is indicated at 20 are secured as by welding, bolts or clamps around the exterior surface of the enclosure 10 adjacent each of the rings to facilitate the attachment of the enclosure to the interior surfaces of each of the rings. As shown in phantom lines at 24, support elements may be provided intermediate the ring attachment portions to minimize any outward deflection of the wall members during the rotation of the enclosure 10. It will be understood of course, that such supports would be provided between each wall section and the associated ring.

To centrifugally cast a concrete beam of square cross section and flat interior and exterior surfaces, the present invention provides a plurality of core members carried within the enclosure 10 as illustrated in FIG. I at 26, 27, 28 and 29. Each core member is formed with a set of outer surfaces as at 30 and 32 and a set of inner surfaces as at 34 and 36. The core members may be constructed of metal plates that are welded together along their edges and provided with strut supports on its interior (FIG. 4) to provide rigidity to each core member at points intermediate the end plates of each member.

Turning now to FIG. 2, there is illustrated an end I view in elevation looking down the axis of rotation indicated at 38 of the enclosure 10. Each end of the core members is secured to the ends 40 of the enclosure 10 by a plurality of L-shaped brackets, one of which is indicated at 42. One end of each bracket is secured to the end plate of a core member and the other end of the will accurately maintain the respective core members stationary with respect to the interior surfaces of the.

wall sections during the centrifuging operation. While the bracket mountings for core members 28 and 29 are not illustrated in FIG. 2, it will be understood that these latter core members are secured in the same manner as core members 26 and 27.

As shown in FIG.- 2 the sets of inner surfaces of the core members consisting of surfaces 34 and 36 are central opening extending along the entire length of the enclosure 10. The generally opposing surfaces 34 and 36 of each of the core members are tapered slightly in the direction of the respective inner surfaces of the wall sections to form trough-like flow passages. The opposite ends of the enclosure 10 are closed and sealed by plate members, one of which is illustrated in FIG. 5 at 44, each of which is bolted to the ends of the wall sections. These plate members are similar with the exception that one of them is provided with an opening 46 through its center of size permitting insertion of a feed conveyor therethrough. The conveyor may consist simply of a tubular conduit or, if desired, an extensible belt conveyor may be utilized to supply cementitious material to the interior of the enclosure 10 along axis Preferably, however, spacer members or headers are employed in place of the plate members 44. With reference to FIG. 3, there is shown in section the disposition of a portion of a header which in one form may be a square metal frame member which snugly interfits between the interior surfaces of the enclosure and exterior surfaces 30 and 32 of all of the core members as shown in FIG. 2 and which functions as a dam to retain the slurry in the enclosure. A similarly formed frame member or header is, of course, positioned in the opposite end of the enclosure 10. To those skilled in this art, it will be clear that by transversely shifting the position of the headers 45 with respect to the longitudinal axis 38 of the enclosure and relative to each other, the longitudinal dimensions of the article to be cast can be varied as desired.

Each of the rings 18 is supported in a vertical position on a pair of spaced apart rollers 48 and 50 which in turn are rotatably mounted on supports 52 and 54 respectively, a pair being provided for each ring. As shown in FIG. 3, each of the rings 18 is formed about its exterior circumference with guide construction in the form of a channel 56 which functions as a bearing surface for the rollers. A base platform 58 is provided on which the supports 52 and S4 for the rollers are mounted. Two perpendicularly extending posts 60 and 62 are also mounted on this base platform 58 on opposite sides of the enclosure 10 and spaced apart so that one post is adjacent a ring at one end of the enclosure and the other adjacent the opposite end thereof.

spaced radially outwardly from the axis 38 to provide a As illustrated in FIGS. 2 and 3, a pair of booms 64 are pivotally mounted on a pin 66 at the top end of posts 60 and 62. Each of the booms is provided with extensible portions 70 and 72 which may be the piston rods of hydraulic cylinders located within the booms 64. Preferably, a bar 68 is attached as by welding transversely across the piston rods 70 and 72. Suitable fluid conduits 74 may be connected to each of the cylinders of the booms 64 to control the extension of the rods 70 and 72. In an alternate embodiment, a single cylinder and piston may be provided with one end of the cylinder pivotally mounted on pin 66 and with the piston rod connected to bar 68 with the rods 70 and 72 freely slidable within bores formed in boom 64. It should be understood that the foregoing description of boom 64 on post 60 applies also to the booms mounted on 'the other posts as at 62 which extend from plateform 58.

As viewed in FIG. 2, idler rollers 78 on the right hand side of axis 38 and 82 on the left hand side are rotatably mounted on shafts 80 and 84 respectively which in turn are mounted on the ends of the extensible rods 70 and 72.

Rollers 48, on the left hand side of axis 38, are each drivingly connected by a drive shaft 49 which extends through each of the rollers mounted on the supports 52 carried by platform 58. As shown schematically in FIG. 2, shaft 49 is rotatably driven through belt 86 which in turn is connected to the output of a conventional rotary power source such as motor 88. The motor of course may be located in any suitable position.

In the operation of the apparatus as thus far described, the ends of the enclosure are closed off by the headers 45 or sealed by the plate members 44 which are securely bolted onto the exterior surfaces of the wall sections of the enclosure. WIth the respective rollers 78 and 82 in engagement with the channels of the rings 18, rotation of the'enclosure about axis 38 is effected upon actuation of motor 88. Thereafter, cement material, in a fluid state, is supplied to the interior of the enclosure along axis 38 by a conveyor that is inserted between the core members or through aperture 46 in one of the plate members 44 if such are used. Due to the centrifugal forces arising by virtue of the rotation of the enclosure 10, the casting material will be forced through the passages formed by the surfaces 36 and 34 of the core members to fill the spaces between the outer surfaces of the core members and the interior surfaces of the wall sections. The interior surfaces of the article being cast with the core members disposed as illustrated in enclosure 10, will be substantially flat and the corners of the article will be substantially rightangled. It should be understood, however that other geometric relationships can be utilized within the scope of the present invention.

In FIG. 4, there is illustrated one of the core members of the present invention showing the disposition of two of the strut elements 90 disposed on the interior of the core member. The strut elements 90 comprise quadrilateral shaped metal plates which are spaced evenly along the longitudinal axis of the core member. The core members may be modified as shown with respect to member 28 to enable the apparatus of the present invention to be utilized in the centrifugal casting of concrete panels by attaching blockout members indicated at 92 in phantom lines to the corners of each of the core members so that the blockout members will be disposed as shown in FIG. 2 with respect to the wall sections of the enclosure 10. With this arrangement, four individual panels may be cast simultaneously when the blockouts 92 are secured to the corner of the outer surfaces of each of the core members as illustrated in FIG. 4. If desired, the blockouts 92 may be bolted directly to the interior of the enclosure. It will be evident that by attaching the blockouts 92 only to the corners of the outer surfaces of oppositely disposed core members, for example 27 and 28 in FIG. 2, L- shaped beams can be cast.

From the foregoing description it can be readily appreciated that by varying the exterior shape of the core members, any desired shape may be imparted to the article being cast. In addition, the thickness of the cast article can be varied by selectively positioning the outer surfaces of the core members with respect to the inner surfaces of the wall sections. Also, steel reinforcing bars or wires, if desired, may be located under tension in the enclosure to be molded in the object being cast or simply suspended therein.

While the invention has been particularly shown and described with reference to the foregoing preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. Apparatus for the centrifugal casting of articles of the type having generally flat, oppositely facing, first and second surfaces, said apparatus comprising:

means defining a first molding element for forming the first surface of an article including a plurality of interconnected wall members mounted on support means having an axis of rotation, said wall members extending generally parallel to said axis with each wall member being spaced substantially equidistantly therefrom,

means defining a second molding element for forming the second surface of the article including a plurality of core members having inner and outer surfaces, said outer surfaces being substantially flat, means for positioning said core members with a said outer surface spaced from and extending in a plane generally parallel to a said wall member, and with said inner surfaces of a said core member spaced from the inner surfaces of adjacent core members to define a flow passage extending generally radially from said axis of rotation to the space between said wall members and said outer surfaces of said core members, and

means for rotating said support means about said axis of rotation.

2. The apparatus as claimed in claim 1 wherein said plurality of said wall members are each joined to an adjacent wall member along an edge which extends generally parallel to said axis of rotation to form an enclosure surrounding said axis, each wall member on one side of said axis extending in parallel relation to a wall member on the opposite side of said axis, said enclosure having a first end and a second end spaced from said first end along said axis of rotation.

3. The apparatus as claimed in claim 2 wherein said core members and said enclosure have opposite ends and said opposite ends of said core members are secured to said opposite ends of said enclosure by a plurality of bracket elements.

4. The apparatus as claimed in claim 2 wherein said support means includes a plurality of annular rings spaced along said axis of rotation with the center of each coinciding with said axis, and each of said rings is formed with an interior and exterior surface, said enclosure having exterior portions which are attached to portions of said interior surfaces of each of said rings, the exterior surfaces of each of said rings having channels extending about their circumferences, said support means further including a base having a set of rollers rotatably carried thereon, in spaced apart relation for engaging said channels of said rings.

5. The apparatus as claimed in claim 4 wherein said rollers are arranged in pairs spaced along said axis with the rollers of a said pair being disposed on either side of said axis to engage and support at spaced points one of said rings.

6. The apparatus as claimed in claim 5 wherein a second set of rollers, in pairs, is provided with the rollers of a said pair being disposed on either side of said axis and rotatably mounted on a shaft extending through each of the rollers on a said side, each of said shafts being carried on the end of a pivotable and extensible boom said booms for each shaft being disposed on either side of said axis so that said rollers of a pair of said second set are positionable in engagement with said channels of said rings at spaced points on a said ring remote from the said points engaged by said pairs of rollers of said first mentioned set.

7. The apparatus as claimed in claim 5 wherein a drive shaft is provided for drivingly connecting the said rollers on said base on one side of said axis and a motor is provided for rotating said drive shaft.

8. The apparatus as claimed in claim 2 wherein means are provided for preventing flow of casting material out of said ends of said enclosure, said means comprising a pair of frame members each having crosssectional dimensions such that said frame members will closely interfit between the interior surfaces of said enclosure and the outer surfaces of said core members.

9. The apparatus as claimed in claim 2 wherein closing means are provided which comprise first and second plates removably and sealingly attachable to said opposite ends of said enclosure, one of said plates having an opening through its center for receiving casting material into said enclosure.

10. Apparatus for the centrifugal casting of articles of the type having generally flat,-oppositely facing first and second surfaces, said apparatus comprising:

a plurality of planar wall members for forming the first surface of an article, each of said wall members being joined to an adjacent wall member along an edge to form an enclosure, said enclosure being mounted on a support having a generally horizontally extending axis of rotation, each wall member on one side of said axis being disposed in parallel relation to a wall member on the opposite side of said axis, each of said parallel disposed wall members being spaced substantially equidistantly from said axis, said enclosure having a first and a second end spaced from said first end along said axis of rotation, and

a plurality of core members having inner and outer define a flow passage extending generally radially' from said axis of rotation to the space between said wall members and said outer surfaces of said core members,

dam means positionable in spaced apart relation along said axis and said outer surfaces of said core members,

said support for said enclosure comprising a plurality of annular rings spaced along said axis of rotation of said enclosure with the center of each of said rings coinciding with said axis,.each of said rings having an interior and exterior surface, said enclosure having exterior portions attached to portions of said interior surfaces of each of said rings, said exterior surfaces of each of said rings having channels extending about their circumferences, a base having a first set of rollers rotatably carried thereon, said first set of rollers being arranged in pairs spaced along said axis with the rollers of a said pair being disposed on either side of said axis to engage and support, at spaced points, one of said rings, and a second set of rollers being arranged.in pairs with each roller of a pair being rotatably mounted on a shaft which is carried on a pivotable and extensible boom, said booms for each shaft being disposed on either side of said axis and said pairs of rollers of said second set being spaced along said axis so'that said rollers of a pair of said second set are positionable in engagement with said channels of said rings at spaced points on a said ring remote from the said points engaged by said pairs of rollers of said first set,

means for rotating the said rollers one of said sets which are located on one side of said axis including a drive shaft connected to each of the last-mentioned rollers and a motor for rotating said shaft so that, when said last-mentioned rollers are driven by said motor, said enclosure will be rotated about said axis. 

1. Apparatus for the centrifugal casting of articles of the type having generally flat, oppositely facing, first and second surfaces, said apparatus comprising: means defining a first molding element for forming the first surface of an article including a plurality of interconnected wall members mounted on support means having an axis of rotation, said wall members extending generally parallel to said axis with each wall member being spaced substantially equidistantly therefrom, means defining a second molding element for forming the second surface of the article including a plurality of core members having inner and outer surfaces, said outer surfaces being substantially flat, means for positioning said core members with a said outer surface spaced from and extending in a plane generally parallel to a said wall member, and with said inner surfaces of a said core member spaced from the inner surfaces of adjacent core members to define a flow passage extending generally radially from said axis of rotation to the space between said wall members and said outer surfaces of said core members, and means for rotating said support means about said axis of rotation.
 2. The apparatus as claimed in claim 1 wherein said plurality of said wall members are each joined to an adjacent wall member along an edge which extends generally parallel to said axis of rotation to form an enclosure surrounding said axis, each wall member on one side of said axis extending in parallel relation to a wall member on the opposite side of said axis, said enclosure having a first end and a second end spaced from said first end along said axis of rotation.
 3. The apparatus as claimed in claim 2 wherein said core members and said enclosure have opposite ends and said opposite ends of said core members are secured to said opposite ends of said enclosure by a plurality of bracket elements.
 4. The apparatus as claimed in claim 2 wherein said support means includes a plurality of annular rings spaced along said axis of rotation with the center of each coinciding with said axis, and each of said rings is formed with an interior and exterior surface, said enclosure having exterior portions which are attached to portions of said interior surfaces of each of said rings, the exterior surfaces of each of said rings having channels extending about their circumferences, said support means further including a base having a set of rollers rotatably carried thereon, in spaced apart relation for engaging said channels of said rings.
 5. The apparatus as claimed in claim 4 wherein said rollers are arranged in pairs spaced along said axis with the rollers of a said pair being disposed on either side of said axis to engage and support at spaced points one of said rings.
 6. The apparatus as claimed in claim 5 wherein a second set of rollers, in pairs, is provided with the rollers of a said pair being disposed on either side of said axis and rotatably mounted on a shaft extending through each of the rollers on a said side, each of said shafts being carried on the end of a pivotable and extensible boom said booms for each shaft being disposed on either side of said axis so that said rollers of a pair of said second set are positionable in engagement with said channels of said rings at spaced points on a said ring remote from the said points engaged by said pairs of rollers of said first mentioned set.
 7. The apparatus as claimed in claim 5 wherein a drive shaft is provided for drivingly connecting the said rollers on said base on one side of said axis and a motor is provided for rotating said drive shaft.
 8. The apparatus as claimed in claim 2 wherein means are provided for preventing flow of casting material out of said ends of said enclosure, said means comprising a pair of frame members each having cross-sectional dimensions such that said frame members will closely interfit between the interior surfaces of said enclosure and the outer surfaces of said core members.
 9. The apparatus as claimed in claim 2 wherein closing means are provided which comprise first and second plates removably and sealingly attachable to said opposite ends of said enclosure, one of said plates having an opening through its center for receiving casting material into said enclosure.
 10. Apparatus for the centrifugal casting of articles of the type having generally flat, oppositely facing first and second surfaces, said apparatus comprising: a plurality of planar wall members for forming the first surface of an article, each of said wall members being joined to an adjacent wall member along an edge to form an enclosure, said enclosure being mounted on a support having a generally horizontally extending axis of rotation, each wall member on one side of said axis beIng disposed in parallel relation to a wall member on the opposite side of said axis, each of said parallel disposed wall members being spaced substantially equidistantly from said axis, said enclosure having a first and a second end spaced from said first end along said axis of rotation, and a plurality of core members having inner and outer surfaces, said core members having opposite ends secured to said first and second ends respectively of said enclosure by a plurality of bracket elements with said outer surfaces spaced from and extending in planes generally parallel to said wall members and with said inner surfaces spaced from the inner surfaces of an adjacent core member to define a flow passage extending generally radially from said axis of rotation to the space between said wall members and said outer surfaces of said core members, dam means positionable in spaced apart relation along said axis and said outer surfaces of said core members, said support for said enclosure comprising a plurality of annular rings spaced along said axis of rotation of said enclosure with the center of each of said rings coinciding with said axis, each of said rings having an interior and exterior surface, said enclosure having exterior portions attached to portions of said interior surfaces of each of said rings, said exterior surfaces of each of said rings having channels extending about their circumferences, a base having a first set of rollers rotatably carried thereon, said first set of rollers being arranged in pairs spaced along said axis with the rollers of a said pair being disposed on either side of said axis to engage and support, at spaced points, one of said rings, and a second set of rollers being arranged in pairs with each roller of a pair being rotatably mounted on a shaft which is carried on a pivotable and extensible boom, said booms for each shaft being disposed on either side of said axis and said pairs of rollers of said second set being spaced along said axis so that said rollers of a pair of said second set are positionable in engagement with said channels of said rings at spaced points on a said ring remote from the said points engaged by said pairs of rollers of said first set, means for rotating the said rollers one of said sets which are located on one side of said axis including a drive shaft connected to each of the last-mentioned rollers and a motor for rotating said shaft so that, when said last-mentioned rollers are driven by said motor, said enclosure will be rotated about said axis. 